Wireless communication systems are well known in the art. Generally, such systems comprise communication stations or units which transmit and receive wireless communication signals between each other. For network systems such as mobile cellular systems, there are typically two types of communication stations, namely, base stations which provide access to the network infrastructure and wireless transmit/receive units (WTRUs) which conduct wireless communications with the base stations.
The term base station as used herein includes, but is not limited to, a base station, Node-B, site controller, access point or other interfacing device in a wireless environment that provides WTRUs with wireless access to a network with which the base station is associated.
The term WTRU as used herein includes, but is not limited to, a user equipment, mobile station, fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. WTRUs include personal communication devices, such as phones, video phones and Internet ready phones that have network connections. In addition, WTRUs include portable personal computing devices, such as PDAs and notebook computers with wireless modems that have similar network capabilities. WTRUs that are portable or can otherwise change location are referred to as mobile units.
Typically, a network of base stations is provided where each base station is capable of conducting concurrent wireless communications with appropriately configured WTRUs. Some WTRUs are configured to conduct wireless communications directly between each other, i.e. without being relayed through a network via a base station. This is commonly called peer to peer wireless communications. WTRUs can be configured for use in multiple networks with both network and peer to peer communications capabilities.
In order to provide global connectivity for wireless systems, standards have been developed and are being implemented. One current standard in widespread use is known as Global System for Mobile Telecommunications (GSM). This is considered as a so-called Second Generation mobile radio system standard (2G) and was followed by its revision (2.5G). GPRS and EDGE are examples of 2.5G technologies that offer relatively high speed data service on top of (2G) GSM networks. Each one of these standards sought to improve upon the prior standard with additional features and enhancements. In January 1998, the European Telecommunications Standard Institute—Special Mobile Group (ETSI SMG) agreed on a radio access scheme for Third Generation Radio Systems called Universal Mobile Telecommunications Systems (UMTS). To further implement the UMTS standard, the Third Generation Partnership Project (3GPP) was formed in December 1998. 3GPP continues to work on a common third generational mobile radio standard.
One type of wireless system, called a wireless local area network (WLAN), can be configured to conduct wireless communications with WTRUs equipped with WLAN modems that are also able to conduct peer to peer communications with similarly equipped WTRUs. A popular wireless local area network environment with one or more WLAN access points, i.e., base stations, is built according to the IEEE 802.11b standard. The wireless service areas for such WLANs may be restricted to specified well defined geographic areas known as “hot spots”. Such wireless communication systems are advantageously deployed in areas such as airports, coffee shops, and hotels. Access to these networks usually requires user authentication procedures. Protocols for such systems are not yet fully standardized in the WLAN technology area, since the IEEE 802 family of standards is evolving.
In order to provide mobility, it is well known to provide battery operated units. As mobile units travel through different wireless service areas or in relation to other WTRUs to which they may directly connect, wireless signal strength and quality will change for a variety of reasons such as relative distance, obstructions and interference from other WTRUs and other sources. Also, in a network setting, a base station may seek to reduce the strength of its signal to a WTRU which is not moving in order to reduce interference to enable an increase in wireless traffic in the particular area.
Reception of wireless signals can be enhanced by providing communication stations with more than one receiver and combining signals received signals processed by the multiple receivers. Communication stations having two receivers generally realize increased signal gain in a combined signal compared to an equivalent single receiver station. Increase gain on the order of 4-7 db is normally achievable where two receivers are used instead of one; even higher gain increases can be realized with more than two receivers. However, using multiple receivers increases a communication station's power consumption, which makes the use of multiple receivers in battery operated mobile units less attractive. The inventors have recognized that it would be desirable to provide a mobile WTRU having enhanced reception capabilities without an inordinate increase in power consumption.